An apparatus for controlling a brushless motor, as an example of rotary electric machines, is commonly designed to use a step-up converter for increasing a DC (Direct Current) voltage to be inputted to an inverter in order to increase a voltage to be applied to the brushless motor. This aims at reducing the effects of a back electromotive force generated by the rotation of the brushless motor at a high RPM.
The conventional structure of the control apparatus however may increase the cost of the control apparatus.
In order to increase a voltage to be applied to the brushless motor without increasing the cost, U.S. Pat. No. 6,320,775 corresponding to Japanese Patent Application Publication NO. H10-337047 discloses a technique that uses a zero-phase circuit of the brushless motor by connecting a battery with a neutral point of the star-connected multiphase windings of the brushless motor; this technique will be referred to as “zero-phase circuit utilization technique hereinafter.